From: Bob Sinclair (bsinclair@netmasterclass.net)
Date: Tue Apr 19 2005 - 18:48:28 GMT-3
Gladston,
Interesting problem. R5 calculates the distance to the ASBR (R4) in two ways:
intra-area across area 200 and inter-area across area 0 and area 300. The
inter-area route to the ASBR is based on R5 getting a Type 4 LSA from R1. I
can find no exception to OSPF's preference for Inter-area routes versus
inter-area routes. The only way I can see to get R5 to prefer the path
through R1 is to make that path also intra-area - using a virtural link to
connect area 0 to R4 across area 300.
If there is another way, I am sure the guys on this list will discover it!
HTH,
Bob Sinclair
CCIE #10427, CCSI 30427, CISSP
www.netmasterclass.net
----- Original Message -----
From: gladston@br.ibm.com
To: Lee Donald
Cc: ccielab@groupstudy.com
Sent: Tuesday, April 19, 2005 4:22 PM
Subject: RE: OSPF - Prefered External Path - Avoid ISDN
When using external type-1, the cost through ISDN is 15xx, and through
serial is 121.
R5-- ------------------bri--ospf a 200--------------------R4
| |
-------ospf a 0-------------R1-----------ospf a 300------
R4 is ASBR, it is connected to area 200 and area 300. It injects route
200.x.x.x
R5 prefers path through ISDN.
Lee Donald <Lee.Donald@t-systems.co.uk>
19/04/2005 17:01
To
Alaerte Gladston Vidali/Brazil/IBM@IBMBR, Lee Donald
<Lee.Donald@t-systems.co.uk>
cc
ccielab@groupstudy.com
Subject
RE: OSPF - Prefered External Path - Avoid ISDN
What is the difference in cost for each route?
-----Original Message-----
From: gladston@br.ibm.com [mailto:gladston@br.ibm.com]
Sent: Tuesday, April 19, 2005 8:53 PM
To: Lee Donald
Cc: ccielab@groupstudy.com
Subject: RE: OSPF - Prefered External Path - Avoid ISDN
Hi Lee, thanks for your time.
If I shutdown the ISDN, R5 uses its serial connected to R1 to reach the
external route.
It seemw OSPF prefers the direct exit. R5 prefers R4 because it just
needs to go through area 200. If BRI is shutdown, R5 goes through area 0
to R1, and from there through area 112 to reach external route.
I am using external type 2, so the cost is always the same, no matter the
internal cost.
But I tried external type 1; even though the cost through ISDN is higher
in this case, OSPF does not care.
I am wondering if there is a way to configure R5 to choose the longer
path, that is, through R1 (area 0 and area 300)
Cordially
------------------------------------------------------------------
Alaerte Gladston Vidali
IBM Global Services - SO
Tel.55+11+2121-2879 Fax:55+11+2121-2449
Lee Donald <Lee.Donald@t-systems.co.uk>
19/04/2005 16:34
To
Alaerte Gladston Vidali/Brazil/IBM@IBMBR, ccielab@groupstudy.com
cc
Subject
RE: OSPF - Prefered External Path - Avoid ISDN
Gladston,
ISDN interfaces in OSPF have a much higher cost than ser interfaces.
The cost for your isdn should be 1562, so there must be another reason it
prefers the isdn path.
In the database it doesn't show this route from the ser int?
-----Original Message-----
From: gladston@br.ibm.com [mailto:gladston@br.ibm.com]
Sent: Tuesday, April 19, 2005 6:28 PM
To: ccielab@groupstudy.com
Subject: OSPF - Prefered External Path - Avoid ISDN
R5 receives external LSA about route 200.200.47.0 from R4 (BRI) and from
R1
(serial).
Is there a way to configure R5 so it prefer path R5---R1 to reach net
200.200.47.0, instead path R5----R4 (bri)?
R4(bri)----OSPF A300---(bri)R5(s0/0)----OSPF A0----(s0/0)R1(s0/0.14)
| |
|___________________________OSPF A200_________________________|
It seems there is a problem with R4, because it is connected to two areas
(area 300 and area 200) while not connected to area0. Would you agree?
Even
though I configure virtual link on R4--R5, this way connecting R4 to area
0,
would you have a solution to the first question? (R5 should prefer the
path
to R1 to reach the external network injected by R4 instead of the
directly
path to R4 (BRI).
show ip ospf database external 200.200.47.0
200.200.47.0 142.20.4.1 294 0x80000005 0x006142 0
Rack2R5#sir 200.200.47.0
Routing entry for 200.200.47.0/24
Known via "ospf 1", distance 110, metric 1582, type extern 1
Redistributing via eigrp 10
Advertised by eigrp 10 metric 10000 1000 255 1 1500
Last update from 200.20.45.5 on BRI0/0, 00:05:41 ago
Routing Descriptor Blocks:
* 200.20.45.5, from 200.20.4.1, 00:05:41 ago, via BRI0/0
Route metric is 1582, traffic share count is 1
Rack2R5#sh ip os border-routers
OSPF Process 1 internal Routing Table
Codes: i - Intra-area route, I - Inter-area route
i 200.20.4.1 [1562] via 200.20.45.5, BRI0/0, ASBR, Area 113, SPF 23
Rack2R5#conf t
int bri 0/0
shutdown
Rack2R5#sir 200.200.47.0
Routing entry for 200.200.47.0/24
Known via "ospf 1", distance 110, metric 148, type extern 1
Redistributing via eigrp 10
Advertised by eigrp 10 metric 10000 1000 255 1 1500
Last update from 200.20.125.1 on Serial0/0, 00:00:03 ago
Routing Descriptor Blocks:
* 200.20.125.1, from 200.20.4.1, 00:00:03 ago, via Serial0/0
Route metric is 148, traffic share count is 1
Rack2R5#sh ip os border-routers
OSPF Process 1 internal Routing Table
Codes: i - Intra-area route, I - Inter-area route
I 200.20.4.1 [128] via 200.20.125.1, Serial0/0, ASBR, Area 0, SPF 31
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